Sealing material for vacuum vessels



May 23, 1939. K. LENZ ET AL .SEALING MATERIAL FOR VACUUM VESSELS Filed Dec. 2, 1937 MM v F 82 0 F n e t Oeo r e t t .l. v U n h rm r T W Cal Patente d May 23, 1939 UNITED STATES PATENT OFFICE SEALING MATERIAL FOR VACUUM VESSELS Kurt Lenz. Berlin-Lichterfelde,- an d Ernst Woeckel, Berlin-Friedenau, Germany, assignors to General Electric Company, a corporation of New York Application December 2, 1937, Serial No. 177,775

In Germany February 2, 1937 i 3 Claims.

jected to high temperatures during the course 5 of manufacture or operation.

In the manufacture of incandescent lamps, Vacuum tubes and many other enclosed electrical devices, it is necessary to take great care to avoid contamination of electrodes orother enclosed parts by deposition of foreign substancesthereon.

.Where the enclosing vessel is constituted of separate metal parts joined by a sealing material, the aforementioned consideration imposes definite I limitations on the character of the sealing materials which may be satisfactorily employed. For

electrode surfaces occurs during the bake-out or degassing processes to which such devices are customarily subjected.

It is an object of the present invention to provide sealing materials which are not subject to appreciable vaporization even when heated to the temperatures ordinarily employed in bake-out processes.

This object is fulfilled in accordance with the invention by employing as a joining material for the metal parts of vacuum vessels a eutectic alloy of a metal or metals of the iron group (i. e., iron, nickel, and cobalt) with tantalum. By the term feutectic alloy is meant an alloy having the lowest possible melting point for the given'constituents. Such alloys are found to have good joining and sealing properties andare further characterized by being only slightly'vaporizable at the tantalum and 60% iron issuitable. For 1370 C.

O a nickel-tantalum alloy with about 38% tantalum and about 62% nickel is suitable. It is also possible to use an alloy of about 40% nickel and f 60% tantalum, having a melting point of about l objectionable vaporization of the solder on to the Due to the inherent brittleness of the alloys described in the foregoing it is advantageous to utilize them in a pulverized state. Thus in performing sealing operations, a paste may be formed by combining the pulverized alloy with a readily evaporating liquid binder such as alcohol or purified petroleum. This paste is then placed I in suitable grooves or indentations formed between the metal parts to be joined and the assembly heated to cause evaporation of the binder. As the temperature is raised to a still higher value the residual powder melts and joints the metal parts in hermetically sealed relationship. In the single figure of the drawing we have indicated the application of .the invention in connection with a vacuum tube of the all-metal type. This comprises an evacuated metal shell 1 containing electrodes which include an anode 2 and a cathode 3. The lower end of the envelope is flanged and is closed by means of a transverse metal header 4 which is joined to the flange. In accordance with our invention the joint be.- tween the flange and the header is sealed by means of one of the sealing alloys described in the foregoing. Such an alloy, whose presence in the sealed joint is indicated at 5, possesses sufficiently low vapor pressure to avoid the danger of contaminating the electrode elements during fabrication or operation of the device.

The invention can be used not only for joining metal parts of electric vacuum vessels but also for other special vacuum vessels such as transportation tanks for rare gases.

What we claim as new and desire to obtain by Letters Patent of the United States is:

1. An electrical discharge device comprising a sealed vessel enclosing electrode structure which is subject to contamination by metallic vapors, metal parts forming constituent elements of the vessel, and a metallic sealing material hermetically joining the metal parts and at least partially exposed to the interior of the vessel, said material consisting essentially of a eutectic alloy of at least one metal of the iron group with tantalum.

2. The combination of claim 1 in which the sealing material consists of approximately 60%, iron and 40% tantalum.

3. The combination of claim 1 in which the sealing material consists of approximately 62% nickel and 36% tantalum.

KURT LENZ. ERNST WOECKEL. 

